Patent EA-000977-B1 (EA)
Title: Oriented polymeric products
Inventor: JAERVENKYLAE JYRI JAAKKO
IPC: B29C48/94
Filed: 1996-06-26
Abstract: 1. A method of forming and continuously orienting an article comprising a crystalline or semi-crystalline thermoplastic polymeric material(s) at a temperature greater than the crystalline melting temperature of said material(s), characterized by the steps of: -adding a chemically reactive substance(s) to the polymeric material before or during forming of either the entire product, or to one or more layers of a multilayer product, or to axial or helical stripes of the product, or to certain segments of the product in the axial direction; -plasticizing and forming a parison of the polymeric material(s) thus prepared at a temperature not high enough to activate the reaction of the said reactive substance(s); -optionally, inducing shear at least to the layer(s) where the chemically reactive substance(s) have been added to and/or stretching the still soft parison in one or both of two directions, simultaneously or stepwise, said stretching including axial draw to effect thermoplastic orientation of the material in the longitudinal direction of the parison and/or radial expansion to effect thermoplastic orientation of the material in the hoop direction of the parison; -decreasing the mobility of the molecules in the layer(s) to be oriented by activating a chemical reaction between the chemically reactive substance(s) and the polymeric material(s) having the chemically reactive substance(s) added thereto when the polymeric material(s) still is/are in a molten state; -inducing shear at least to the product, layer(s), stripes, or segments to which the chemically reactive substance(s) have been added and/or stretching the still soft, at least partly reacted parison in one or both of two directions, simultaneously or stepwise, said stretching including axial draw to effect orientation of the material in the longitudinal direction of the parison and/or radial expansion to effect orientation of the material in the hoop direction of the parison; -calibrating and cooling the parison in the oriented condition to make the orientation permanent at least in the layer(s) where the chemical reaction(s) has taken place. 2. The method of claim 1, characterized in that the said chemically reactive substance(s) when activated causes a reaction with the polymeric material(s) so that the new molecules have decreased mobility in the molten state because of steric hindrance. 3. The method of claim 1 or 2, characterized in that the said chemically reactive substance(s) comprises a cross-linking agent which is able to cross-link the polymer molecule chains. 4.The method of any of claims 1 to 3, characterized in that the reaction needed for getting the material in permanently orientable state is activated with additional heat or radiation after initial thermoplastic orientation. 5. The method of any of claims 1 to 4, characterized in that the mobility of the molecular chain is reduced at least in one of the layers close to or in the one to be oriented by the addition of inorganic or organic flake minerals or fibres or such material which will fibrillate during orientation. 6. The method of any of claims 1 to 5, characterized in that the melt strength of the parison, needed for the axial and/or radial draw, is improved by the addition to one or more parts of the product of organic and/or inorganic fillers, for example, fibres or flake shaped minerals, which can also be oriented and which act like nucleating agents for the oriented crystallites if blended to the material in the oriented layer. 7. The method of any of claims 1 to 6, characterized in that at least to the layers close to the or each layer to be oriented fibres and/or minerals have been added which respond to dielectric heating and this heat is used to rapidly increase the temperature in the layer containing the reactive substance(s) for the activation of the reaction(s). 8. The method of any of claims 1 to 7, characterized in that at least to the layers not to be oriented organic and/or inorganic fibres or flake shaped minerals up to 10-50 % by weight have been added and/or said layer is further cross-linked, with the same cross-linking method as during drawing or by another method, during the process and after it has reached its final dimensions to an additional gel content level of up to 80 %. 9. The method of any of claims 1 to 8, characterized in that the parison is first stretched in a thermoplastic state in order to get the molecular chains structured and substantially aligned and then again during/after the reaction phase, and this total draw, at least in the axial direction is up to 600%. 10. The method of any of claims 1 to 9, characterized in that the article is bidirectionally oriented, and the parison is extruded as a tubular member having a relationship between wall thickness and diameter which is greater than 2:100 and the axial and hoop orientations are in the same or different layers of the product. 11. The method of claim 10, characterized in that the tubular member is exposed after initial orientation inside an extrusion tool to free axial and or radial expansion which is facilitated by maintaining a differential fluid pressure over the wall of the tubular member. 12. The method of any of claims 1 to 11, characterized in that the article is blow moulded, and after leaving a die set, the parison is further stretched and oriented by blowing it into a cavity and the internal overpressure is fed into the cavity through an extruder. 13. The method according to any of claims 1 to 10, characterized in that the article is injection moulded. 14. The method of any of claims 1 to 11, characterized in that the parison is pressed during further cross-linking against mould(s), which can be moving with said member, and said moulds are heated for holding the material at a cross-linking temperature. 15. The method of any of claims 1 to 11, characterized in that the orientation is effected in a closed die set. 16. The method of any of claims 1 to 11, characterized in that the parison is exposed to radial expansion on a continuously or stepwise enlarging mandrel by drawing the parison over the mandrel. 17. The method of any of claims 1 to 11, 15 and 16, characterized in that the parison is enclosed by a jacket which is either heated or cooled and the material of the parison pushed with extrusion pressure through a die cavity, defined by the said mandrel and the said jacket, and the material is radially oriented within the die cavity and the axial draw, if any, is applied to the enlarged extrudate exiting the die cavity. 18. The method of any of claims 1 to 11 and 15-17, characterized in that the parison is cooled internally within a die set with an integral cooling mandrel, of substantially the same diameter as the stretching mandrel, and which may extend out of the die set. 19. The method of any of claims 1 to 11 and 15 to 18, characterized in that the mobility of the molecule chains is reduced and hence the die swell is decreased by immediate slight cooling of the parison, coming out of a die set, with a water spray or an air flow before entering a calibration sleeve. 20. The method of any of claims 1 to 19, characterized in that the extent to which the product is crosslinked and oriented is partly controlled by choosing the starting point of cooling in relation to the point where the final dimension of the product is reached, for example, by closing or activating cooling media circuits coupled to the jacket and mandrel of claim 15. 21. The method of any of claims 1 to 20, characterized in that the plastics material to be crosslinked is a polyolefin composition comprising a higher melt flow rate olefin polymer or co-polymer having an average molecular weight (Mw) ranging from 30,000 to 1,000,000 g/mol and a lower melt flow rate olefin polymer or co-polymer having a molecular weight greater than 600,000 g/mol, where the difference in viscosity is at least ten fold. 22. A method for the production of an oriented crystalline or semi-crystalline thermoplastic polymeric article which comprises: (i) heating a crystalline or semi-crystalline thermoplastic polymeric material to a temperature at or above its crystalline melting point; (ii) forming the polymeric material into an article whilst at a temperature at or above its crystalline melting point; (iii) subjecting the polymeric material to shear forces and/or stretching, either during or after the formation of the hollow tubular article to effect orientation of the polymeric material in the longitudinal and/or transverse directions; (iv) reacting the polymeric material either before, during, or after the formation of the article, and either before or during orientation, or after orientation but before substantial relaxation of the orientation has taken place, with a crosslinking agent, or a grafting agent whereby steric hindrance of polymer chain movement is increased; the resultant article having a tensile strength in the direction or directions of orientation greater than the tensile strength of an unoriented article formed from the same polymeric material. 23. A method according to claim 22, wherein the article is an elongate hollow article. 24. A method according to claim 22 or 23, wherein the article is a hollow tubular article formed by extrusion. 25. A method according to any of claims 22 to 24, wherein the polymeric material is mixed with the crosslinking agent or grafting agent within an extruder. 26. A method according to any of claims 22 to 25, wherein the article has a wall thickness of greater than 0.8mum, preferably greater than 2mm. 27. A method according to any of claims 22 to 26, wherein orientation is effected in both the longitudinal and the hoop directions. 28. A method according to any of claims 22 to 27, wherein the thermoplastic crystalline polymeric material is reacted with the crosslinking agent or the grafting agent in a first stage and then subjected to shear forces and/or stretching to effect orientation